General Introduction

The earth’s energy balance is dominated by atmospheric heat trapping; about 70% of of the incoming solar energy is absorbed. The absorbed energy is re-emitted at infrared wavelengths by the atmosphere and the earth’s surface. Most of the surface radiation is trapped by clouds and greenhouse gases, and returned to the earth. This phenomenon is called the greenhouse effect, inducing an average temperature of the earth at the surface of +15 °C rather than the -18 °C it would have without the heat trapping. This greenhouse effect is essential for the existence of life on earth, having made it possible for millions of years.